With the development and popularization of battery electric vehicles/hybrid electric vehicles at present, quickly and effectively pre-charging the power battery system of an electric vehicle has become increasingly important.
An electric drive system of the existing electric vehicle typically includes a battery pack sub-system and a motor sub-system, wherein the battery pack sub-system usually includes a battery pack, a battery management system and a distribution box, while the motor sub-system usually includes an inverter and a motor.
FIG. 1 is a schematic drawing of a battery pack sub-system of an existing power battery pre-charge system for an electric vehicle. As shown in FIG. 1, the battery pack sub-system includes a battery pack 1 and a distribution box 2, wherein said battery pack 1 further includes a plurality of battery management units 3 and a plurality of electric cores 4, said plurality of electric cores 4 are connected in series to form a high-voltage battery, and said battery management units 3 are used for monitoring voltages, currents, capacities, etc. of said plurality of electric cores 4. The distribution box 2 is used for controlling on and off of connection of the battery pack sub-system to the outside, and the electrical connection thereof typically consists of a main positive relay Relay+, a main negative relay Relay−, a pre-charge relay Pre-charge, and a pre-charge resistor R_precharge (wherein, B+ is a positive electrode of the battery, B− is a negative electrode of the battery, P+ is an output positive electrode of the battery pack, P− is an output negative electrode of the battery pack). As shown in FIG. 1, the existing power battery pre-charge system for an electric vehicle has the following working principle: during power-up, the main negative relay Relay− is closed first, then the pre-charge relay Pre-charge is closed, such that a pre-charge loop charges a bus capacitor of the motor sub-system (e.g. typically charging the bus capacitor by a first order resistance-capacitance circuit), thus avoiding burning of the relay and the inverter due to the large transient charging current generated by directly closing the main positive relay, subsequently, when a predetermined condition is met, the pre-charge process is ended and the main positive relay Relay+ is closed for charging.
However, the above existing technical solution has the following problems: (1) a resistance-capacitance charging structure is used, so a voltage difference on the resistor becomes smaller in the later stage of charging and the charging current decreases exponentially, resulting in long charging time and low charging efficiency; (2) electrical distribution devices like a relay are usually disposed in a distribution box, while addition of the pre-charge relay and pre-charge resistor results in an increase in the cost of the distribution box and makes the small space in the distribution box even more cramped, besides, the pre-charge resistor acts as a heating device during each pre-charge, so the failure rate of the whole distribution box increases remarkably, and the burden of system control and diagnosis increases as well; (3) the pre-charge resistor needs to withstand the high voltage of the entire battery pack when the relay is just closed, so it is hard to select the pre-charge resistor, namely, if a resistor of a corresponding rated power is selected, since the maximum current exists for a very short time, parameter waste is inevitable, but if a resistor is used exceeding its rated power, when parameters like external capacitance change, overheat of the resistor may occur and failure rate will increase.
Hence, there is a need to provide power battery pre-charge system and device for an electric vehicle, which have high pre-charge efficiency, low cost and low failure rate.